| Discrete multi-tone system having dht-based frequency-domain equalizer -> Monitor Keywords |
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Discrete multi-tone system having dht-based frequency-domain equalizerRelated Patent Categories: Pulse Or Digital Communications, Systems Using Alternating Or Pulsating Current, Plural Channels For Transmission Of A Single Pulse Train, Quadrature Amplitude ModulationDiscrete multi-tone system having dht-based frequency-domain equalizer description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070201574, Discrete multi-tone system having dht-based frequency-domain equalizer. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention generally relates to discrete multi-tone communication systems, and more particularly to a discrete multi-tone communication system using discrete Hartley transform for modulation and demodulation. [0003] 2. The Prior Arts [0004] Discrete multi-tone (DMT) is a multi-carrier modulation (MCM) technique commonly applied in wireline communications such as digital subscriber loops (xDSL) including ADSL, ADSL2, ADSL2+, and VDSL, and power-line communications such as HomePlug. The basic idea of DMT is that a large number of sinusoids (i.e., subcarriers) are modulated by complex-valued quadrature amplitude modulation (QAM) symbols derived from an input bit stream, and transmitted in parallel. Performing a modulation on the complex valued constellation points generates samples of the continuous-time signal to be transmitted during a DMT symbol period. At the receiver, the QAM symbols are recovered by performing a demodulation on the analog-to-digital-converted received signal. A typical DMT system for xDSL is shown in FIG. 1. As illustrated, discrete Fourier transform (DFT) and IDFT (i.e., Inversed DFT) are adopted for baseband demodulation and modulation for the DMT system in the receiving end (Rx) and transmitting end (Tx) (separated by the dashed line in FIG. 1) respectively. A pair of digital-to-analog (D/A) converter and an analog-to-digital (A/D) converter is also provided around the analog communication channel. A time-domain equalizer (TEQ) is used at the receiving end to shorten the channel dispersion and, thereby, minimize intersymbol interference (ISI) caused by channel distortion resulted from, for example, long loop length, gauge variation, and bridge-tap. In addition, to compensate the phase rotation and amplitude distortion existing on each subchannel in the frequency domain, a frequency-domain equalizer (FEQ) is deployed. Also, to guard against the ISI, cyclic prefix (CP) are added and removed at the transmitting end and the receiving end, respectively. [0005] The modulation and demodulation operations performed by the IDFT and DFT can be expressed mathematically as follows: IDFT .times. : .times. .times. x n = 1 N .times. k = 0 N - 1 .times. X k W N - kn , n = 0 , 1 , .times. , N - 1 ( 1 ) DFT .times. : .times. .times. Y k = n = 0 N - 1 .times. y n W N kn , k = 0 , 1 , .times. , N - 1 ( 2 ) where W N = e - j .times. 2 .times. .pi. N , X.sub.k or Y.sub.k is the complex transmission symbol on the k-th subchannel in frequency domain, x.sub.n or y.sub.n is the n-th transmission sample in time domain, and N is the number of points for the IDFT/DFT. [0006] The FEQ or, as it is used behind the DFT, the DFT-based FEQ can be implemented using various algorithms. For example, the MMSE (minimum mean-square error) algorithm tries to minimize the estimated error between the equalized signal and the transmitted signal. Among these algorithms, the LMS (least mean square) algorithm is most popular in terms of VLSI implementation. The LMS algorithm in the DFT-based FEQ consists of three operations: filtering, error estimation, and coefficient updating, expressed mathematically as follows:Filtering: .sub.k=Y.sub.kW.sub.k*=(Y.sub.k,R+jY.sub.k,I)(W.sub.k,R-jW.sub.k,I) (3)Error estimation: E.sub.k=X.sub.k- .sub.k (4)Coefficient Updating: W.sub.k(n+1)=W.sub.k(n)+.mu..sub.kY.sub.kE.sub.k* (5) where the subscripts R and I represent the real part and imaginary part of a complex number respectively, the superscript asterisk (*) denotes the complex conjugate operation, Y.sub.k is the DFT output, X.sub.k is the training symbol of the k-th subchannel of the DMT system, W.sub.k is the FEQ coefficient of the k-th subchannel, and .mu..sub.k is the updating step-size of the FEQ for the k-th subchannel. An embodiment of the DFT-based FEQ is illustrated in FIG. 2. [0007] Prior arts have suggested replacing the DFT with discrete Hartley transform (DHT) so as to reduce the computing complexity from complex to real multiplication involved in DFT, as DHT itself is real-valued operation. With such a substitution, the DFT-based DMT system shown in FIG. 1 would become a DMT system illustrated in FIG. 3, where the modulation at the transmitting end is realized by the inverse DHT (IDHT) with a preceding complex-to-real transformation (C2RT), and the demodulation at the receiving end is realized by DHT with a succeeding real-to-complex transformation (R2CT). C2RT is required to transform the complex symbol X.sub.k into the real symbol H.sub.k; and R2CT is required to transform the real symbol {tilde over (H)}.sub.k to the complex symbol Y.sub.k. Please note that the DFT-based FEQ still has to be adopted in the DHT-based DMT system of FIG. 3, as basically the FEQ architecture remains the same. [0008] The modulation and demodulation operations performed by the IDHT and DHT can be expressed mathematically as follows: IDHT .times. : .times. .times. x N = 1 N .times. k = 0 N - 1 .times. H k cas .function. ( 2 .times. .pi. .times. .times. n .times. .times. k / N ) , n = 0 , 1 , .times. , N - 1 ( 6 ) DHT .times. : .times. .times. H ~ k = n = 0 N - 1 .times. y n cas .function. ( 2 .times. .pi. .times. .times. n .times. .times. k / N ) , k = 0 , 1 , .times. , N - 1 ( 7 ) where cas()=cos()+sin(), and N is the number of points for the IDHT/DHT and is the same as that for the IDFT/DFT. Similarly, the C2RT and R2CT can be expressed as follows:C2RT: H.sub.k=X.sub.k,R-X.sub.k,I (8)R2CT: Y.sub.k=Y.sub.k,R+jY.sub.k,I={tilde over (H)}.sub.k,E-j{tilde over (H)}.sub.k,O (9) where {tilde over (H)}.sub.k,E and {tilde over (H)}.sub.k,O are the even and odd parts of the {tilde over (H)}.sub.k respectively, which can be obtained by: H ~ k , E = H ~ k + H ~ N - k 2 ( 10 ) H ~ k , O = H ~ k - H ~ N - k 2 ( 11 ) SUMMARY OF THE INVENTION [0009] A DMT system is provided herein. As described above, in practice, the IDFT and DFT of a conventional DMT system can be replaced by the IDHT with a preceding complex-to-real transformation (C2RT), and by the DHT with a succeeding real-to-complex transformation (R2CT) at the transmitting end and the receiving end respectively. With the present invention, the DFT and the DFT-based FEQ at the receiving end of a conventional DMT system is replaced by the DHT and a DHT-based FEQ, omitting the use of R2CT. [0010] At the transmitting end, the DMT system of the present invention performs modulation either by IDFT or by the IDHT along with C2RT while, at the receiving end, the demodulation is just realized by the DHT. The DHT-based FEQ directly equalizes each of the 0-th to (N-1)-th, subchannels output from the DHT as R2CT is omitted, where N is the number of points of DHT. Finally, each of the 0-th to (N/2-1)-th subchannels of the DMT system is obtained by combining the k-th and (N-k)-th subchannels of the DHT-based FEQ for k=0, 1, . . . , (N/2-1). [0011] The LMS algorithm can also be adopted for the DHT-based FEQ, which is very suitable for VLSI implementation. The LMS algorithm of the DHT-based FEQ also contains the filtering, error estimation and coefficient updating operations. [0012] The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 is a schematic diagram showing a conventional DFT-based DMT system for xDSL. [0014] FIG. 2 is a schematic diagram showing an embodiment of the DFT-based FEQ of FIG. 1. [0015] FIG. 3 is a schematic diagram showing a conventional DFT-based DMT system for xDSL realized by DHT. [0016] FIG. 4a is a schematic diagram showing a DMT system for xDSL according to a first embodiment of the present invention. [0017] FIG. 4b is a schematic diagram showing a DMT system for xDSL according to a second embodiment of the present invention. [0018] FIG. 5 is a schematic diagram showing an embodiment of the DHT-based FEQ of FIGS. 4a and 4b. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0019] The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. [0020] FIGS. 4a and 4b are schematic diagrams showing a DMT system for xDSL according to two embodiments of the present invention. As illustrated, at the transmitting end, the modulation can be realized either by IDFT alone or by IDHT with a preceding C2RT. In the following, for simplicity, the first embodiment of FIG. 4a will be used as an example. Please note that, even though the application of the present invention to xDSL is presented throughout the specification, the present invention can actually be applied to various communication systems, now known or later developed. Continue reading about Discrete multi-tone system having dht-based frequency-domain equalizer... Full patent description for Discrete multi-tone system having dht-based frequency-domain equalizer Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Discrete multi-tone system having dht-based frequency-domain equalizer patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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